Abstract <p>Magnesium-matrix composite materials reinforced with high-alloy chrome–nickel steel are promising low-density materials with improved strength. To activate the steel surface for liquid-phase formation of steel-reinforced magnesium-matrix composite materials, we propose chloride, chloride–fluoride, and fluoride fluxes such as are widely used in soldering of magnesium alloys. Our results demonstrate how the nature of the flux and process temperature influence the wetting and spreading properties of liquid magnesium on high-alloy austenitic steel. We have identified the most efficient activating flux compositions. Preliminary aluminizing of steel has been shown to ensure a considerable increase in the spreading area of magnesium on austenitic steel.</p>